In the bending of relatively large diameter pipe, bending machines are used wherein the pipe is supported upon a die or support called the holding shoe at one end beneath an upper bending die which is supported in fixed position above the pipe. A movable die called the strongback supports the pipe at the other end of the bending die. The strongback is moved pivotally upward to bend the pipe against the convexly curved lower surface of the bending die.
An internal expandable mandrel is disposed within the pipe to prevent pipe distortion and collapse during bending. The internal mandrel, because of its size and structure, cannot be positioned close to the end of a pipe to be bent, and when the pipe is bent adjacent to one of its ends the pipe end may become distorted or collapsed to an out of round condition.